Bending Stiffness Values Research Articles

Active control for adaptive origami structures undergoing damage

Origami structures, such as those with a Miura-Ori fold pattern, have one principle direction of kinematic freedom where rigid foldability holds true. However, motions such as twisting and curling, and bending require that origami panels bend, thus adding complexity to the system. The goal of this work is to study the actuation of Miura-Ori structures for damage detection. The combination of form-finding for large displacements and finite element model for dynamic characterization is successful to capture the kinematic properties of the Miura-Ori origami structure movements of folding and curling. Simulations and experimental tests are useful as a starting point for determining the behavior of mid-scale actuated origami structures. Stiffness values for folding of creases and bending of panels must be considered when modeling shape change of Miura-Ori origami structures using dynamic relaxation. Energy produced by the folding and bending stiffness values activated in the structure through actuation is a useful measure to rank elements in terms of their potential for damage.

Comparison of Test Methodologies for Computing Bending and Shear Stiffness of Cross-Laminated Timber

Abstract Current testing methods for evaluating the out-of-plane bending and shear stiffness terms of cross-laminated timber (CLT) materials use a relatively long span panel. When new CLT layups and composites are proposed, especially when manufactured from pilot-scale facilities, the length requirement may be a barrier for material property evaluation. The purpose of this paper was to compare current bending and shear stiffness test methods of CLT with alternative forms, including a simultaneous calculation method and the five-point bending test, which uses a shorter beam than current testing methods. Both experimental evaluation and finite element modeling of the mechanical properties were used to compare the proposed test methods. In general, numerical and experimental results demonstrated that effective bending stiffness (EIeff) values of CLT panels evaluated by different test methods were similar (maximum 12.7 % difference). Effective bending and shear stiffness values from the finite element method (FEM) agreed with experimental results. FEM demonstrated that both the simultaneous solution and the five-point bending test can be used as alternative test methods for evaluation of the bending and shear stiffness for CLTs. However, the effective shear stiffness values of CLTs from current industry standards were at least 450 % less than both the experimental evaluation and FEM prediction.

A high-fidelity numerical study on the propulsive performance of pitching flexible plates

In this paper, we numerically investigate the propulsive performance of three-dimensional pitching flexible plates with varying flexibility and trailing edge shapes. We employ our recently developed body-conforming fluid-structure interaction solver for our high-fidelity numerical study. To eliminate the effect of other geometric parameters, only the trailing edge angle is varied from 45° (concave plate), 90° (rectangular plate) to 135° (convex plate) while maintaining the constant area of the flexible plate. For a wide range of flexibility, three distinctive flapping motion regimes are classified based on the variation of the flapping dynamics: (i) low bending stiffness KBlow, (ii) moderate bending stiffness KBmoderate near resonance, and (iii) high bending stiffness KBhigh. We examine the impact of the frequency ratio f* defined as the ratio of the natural frequency of the flexible plate to the actuated pitching frequency. Through our numerical simulations, we find that the global maximum mean thrust occurs near f*≈1 corresponding to the resonance condition. However, the optimal propulsive efficiency is achieved around f* = 1.54 instead of the resonance condition. While the convex plate with low and high bending stiffness values shows the best performance, the rectangular plate with moderate KBmoderate is the most efficient propulsion configuration. To examine the flow features and the correlated structural motions, we employ the sparsity-promoting dynamic mode decomposition. We find that the passive deformation induced by the flexibility effect can help in redistributing the pressure gradient, thus, improving the efficiency and the thrust production. A momentum-based thrust evaluation approach is adopted to link the temporal and spatial evolution of the vortical structures with the time-dependent thrust. When the vortices detach from the trailing edge, the instantaneous thrust shows the largest values due to the strong momentum change and convection process. Moderate flexibility and convex shape help to transfer momentum to the fluid, thereby improving the thrust generation and promoting the transition from drag to thrust. The increase in the trailing edge angle can broaden the range of flexibility that produces positive mean thrust. The role of added mass effect on the thrust generation is quantified for different pitching plates and the bending stiffness. These findings are of great significance to the optimal design of propulsion systems with flexible wings.

A full‐scale study of Darcy‐Weisbach friction factor for channels vegetated by riparian species

AbstractIn this article, an open channel flow resistance equation, deduced applying dimensional analysis and incomplete self‐similarity condition for the flow velocity distribution, was tested using measurements carried out in a full‐scale channel equipped with three types of riparian plants (Salix alba L., Salix caprea L. and Alnus glutinosa L.). In the experimental channel, having banks lined with boulders, the vegetation branches were anchored in a concrete bottom. For each species, the measurements were carried out with plants having different amounts of leaves, different plant density and plant area index. The relationship between the scale factor Γ of the velocity profile and the Froude number was separately calibrated by measurements carried out without and with vegetation. The component of Darcy‐Weisbach friction factor corresponding to the riparian vegetation fv was calculated as the difference between the measured friction factor value (channel grain roughness + vegetation) and that calculated for the channel without vegetation in the same hydraulic conditions. Using these fv values, the relationship between the scale factor Γ and the Froude number was calibrated. In this last relationship, a scaling coefficient a varying with the investigated vegetation type was introduced. This coefficient, as expected, gives the highest friction factor values for vegetation having branches with leaves. The theoretical flow resistance law, coupled with the relationship for estimating the Γ function having a scaling coefficient different for each investigated vegetation type, allowed an accurate estimate of the Darcy‐Weisbach friction factor (errors less than or equal to 20% for 82.6% of the investigated cases). Finally, for the investigated vegetation species that are characterized by a condition with few leaves or leafless, the scaling coefficient a resulted strongly related to the bending stiffness. This analysis demonstrated that the highest Darcy‐Weisbach friction factors correspond to vegetation species characterized by the highest values of bending stiffness. The friction factor values calculated for this last condition are characterized by errors that were less than or equal to ±20% for 90.6% of cases.

Structural Deformation of Existing Horseshoe-Shaped Tunnels by Shield Overcrossing

In urban areas, the construction of subway tunnels is faced with complex crossing problems. The interaction of tunnels with structural deformation has not been comprehensively studied, especially in the construction of new tunnels crossing above existing tunnels. To better predict the structural deformation of the existing tunnels caused by shield excavation, this study used FLAC3D finite difference software, field monitoring, and an analytical method. A numerical model was used to simulate the influence of the shield weight, grouting pressure, and the grout hardening process on the existing tunnel. The results show that the deformation of horseshoe-shaped tunnel structure can be divided into four stages and the corresponding control measures should be taken for each stage to prevent the structural damage. Moreover, the weight of the shield can restrain the existing tunnel from floating up, but it may cause the cracking of the existing tunnel structure without internal steel support. Based on the “two-stage analysis method”, the simplified analytical method solved the additional stress and the uplift deformation in the first stage and second stage, respectively. The proposed analytical method can rapidly estimate the maximum uplift deformation of the existing horseshoe-shaped tunnel with different bending stiffness values under shield excavation.

Harnessing distinct deformation modes of auxetic patterns for stiffness design of tubular structures

Auxetic materials with a negative Poisson's ratio show a unique lateral expansion under tension while their deformation under shear is similar to that of normal materials. Here, we present a novel method to design the stiffness of tubular structures by exploiting these load-dependent distinct deformation modes of auxetic materials. Auxetic cutting patterns are engraved on a tube whose bending and torsional stiffness values are predicted computationally for a comprehensive set of design parameters and measured experimentally for representative designs. Results demonstrate that a wide range of bending and torsional stiffness values can be effectively achieved and controlled independently. The proposed design principle is simple and powerful, and hence can be easily extended to design the mechanical properties of non-tubular structures as well.

Interspecific anatomical differences result in similar highly flexible stems in Bignoniaceae lianas.

Lianas are intriguing forest components in the tropics worldwide. They are characterized by thin and flexible stems, which have been related to a unique stem anatomy. Here, we hypothesized that the anatomical diversity of lianas, varying in shapes, proportions, and dimensions of tissues and cell types, would result in different stem bending stiffnesses across species. To test this hypothesis, we chose four abundant liana species of central Amazonia belonging to the monophyletic tribe Bignonieae (Bignoniaceae) and compared their basal stems for their anatomical architectures and bending properties. Measurements of anatomical architecture and bending stiffness (structural Young's modulus) included light microscopy observations and three-point bending tests, which were performed on basal stems of eight individuals from four Bignonieae species. All analyses, including comparisons among species and relationships between stem stiffness and anatomical architecture, were performed using linear models. Although the anatomical architecture of each species consists of different qualitative and quantitative combinations of both tissues and cell types in basal stems, all species analyzed showed similarly lower bending stiffnesses. This similarity was shown to be directly related to high bark contribution to the second moment of area, vessel area and ray width. Similar values of stem bending stiffness were encountered in four liana species analyzed despite their variable anatomical architectures. This pattern provides new evidence of how different quantitative combinations of tissue and cell types in the basal stems of lianas can generate similarly low levels of stiffness in a group of closely related species.

Trapezoidal core sandwich panel produced with sugarcane bagasse

The properties of traditional particleboards are limited by their flat shape. New shapes and configurations with alternative raw materials enable strength and stiffness gains without significantly increasing weight. In this context, the present work presents an investigation of the potential use of sugarcane bagasse particles agglomerated with castor oil-based polyurethane resin to produce trapezoidal core sandwich panels for building applications. Thickness swelling was analysed based on the Brazilian standard NBR 14810 and flexure tests were performed according to the standard ASTM C393. Maximum force at failure, bending stiffness (EI), maximum moment (FbS), maximum shear stiffness (U), and core shear modulus (G) were calculated. The obtained results were compared with specifications of the standard PS-2-10 – Performance Standard for Wood-Based Structural-Use, which provides values of bending stiffness and maximum moment requirements for OSB panels according to different classes of use. The evaluated sandwich panels presented bending properties (up to 2.1×106 N-mm2/mm for EI and 1199 N-mm/mm for FbS) similar to commercial OSB panels, showing potential for sealing, structural, and flooring applications. The castor oil polyurethane resin presented acceptable efficiency as the particle binder and as an adhesive for the face-core gluing of the low density sandwich panels (0.43 MPa), meeting the minimum requirements recommended by ABNT NBR 14810:2006.

Nondestructive Assessment of Growing Rat Tibial Mechanical Properties Under Three-Point Bending: A Microcomputed Tomography Based Finite Element Study.

Microcomputed tomography (micro-CT) based finite element models (FEM) are efficient tools to assess bone mechanical properties. Although they have been developed for different animal models, there is still a lack of data for growing rat long bone models. This study aimed at developing and calibrating voxel-based FEMs using micro-CT scans and experimental data. Twenty-four tibiae were extracted from rats aged 28, 56, and 84 days old (d.o.) (n = 8/group), and their stiffness values were evaluated using three-point bending tests. Prior to testing, tibiae were scanned, reconstructed, and converted into FEM composed of heterogeneous bone properties based on pixel grayscales. Three element material laws (one per group) were calibrated using back-calculation process based on experimental bending data. Two additional specimens per group were used for model verification. The calibrated rigidity-density (E-ρ) relationships were different for each group: E28 = 10,320·ρash3.45; E56 = 43,620·ρash4.41; E84 = 20,090·ρash2.0. Obtained correlations between experimental and FEM stiffness values were 0.43, 0.10, and 0.66 with root-mean-square error (RMSE) of 14.4%, 17.4%, and 15.2% for 28, 56, and 84 d.o. groups, respectively. Prediction errors were less than 13.5% for 28 and 84 d.o. groups but reached 57.1% for the 56 d.o. group. Relationships between bone physical and mechanical properties were found to change during the growth, similarly to bending stiffness values, which increased with bone development. The reduced correlation observed for the 56 d.o. group may be related to the pubescent transition at that age group. These FE models will be useful for investigation of bone behavior in growing rats.

Distribution of Bending Stiffness of Orthotropic Fibrous Material Based on an Example of Corrugated Board

Commonly known methods for calculating the bending stiffness of corrugated board allow to calculate values related to the machine and cross direction of corrugated board but do not allow to calculate bending stiffness in any intermediate direction. The article presents a method for calculating bending stiffness in any direction in the plane of corrugated board, on the basis of the bending stiffness values in the machine and cross direction. Comparing the results of measurements of bending stiffness in selected directions with those of their calculations, the method proposed was verified and its practical usefulness confirmed.

ДОСЛІДЖЕННЯ ПОКАЗНИКІВ СЕНСОРНОГО КОМФОРТУ ТЕКСТИЛЬНИХ МАТЕРІАЛІВ ДЛЯ ЛІКАРНЯНОЇ ПОСТІЛЬНОЇ БІЛИЗНИ

Investigation of the influence of textile materials structure of different raw materials for hospital bedding on the ability to provide sensory comfort and durability. Theoretical and experimental investigations are based on the main positions of textile materials science. Sensory comfort and durability of textile fabrics were evaluated by thermal and mechanical properties. The measurement of thermophysical characteristics was carried out on the ALAMBETAinstrument, the abrasion resistance was determined on a Pilltester type 14. The strength of textile materials, the tangential resistance, the flexural rigidity and the resistance of dyeing to dry friction were determined by standardized methods. A comparative analysis of the sensory comfort of traditional textile materials for hospital bedding and fabric with bamboo fibers was carried out, which is determined by the mechanospecific sensations of skin receptors on the surface texture of the material, its roughness, stiffness, the feeling of cold or warmness when touching.Their thermophysical properties are determined, the evaluation of the feeling of cold or heat when touched is made according to the indicator "thermal absorption coefficient". By the method of an inclined plane the differences of the texture of dry and moisten studied fabrics was analyzed. The results of the wear resistance indicated that all fabric samples have high abrasion resistance; on part of the test specimens after 1200 cycles appearednap, on mixed fabric – piles.The values of strength and bending stiffness were determined and the effect of 5 washing cycles on these indices was determined. The resistance of the dye to the action of dry friction of all investigated materials is 5 points. The comparative analysis of the values of the coefficients of thermal absorption made it possible to evaluate the feeling of cold or heat when touched, which coincide with the results of the provided organoleptic determinations.It has been experimentally proven that the assortment of cotton and mixed textile fabrics used now for bedding can be supplemented with bamboo fiber materials that provide a high level of sensory comfort and durability. A new range of textile materials for bed linen has been proposed, taking into account the requirements of sensory comfort and durability.

Analytical Method for Local Damage of Beams under Moving Vehicle Loading

In order to accurately identify damage of bridge under natural excitation, an analytical solution of local stiffness of simply supported beam structure is established by using structural mechanics method through establishing the moving load model of simply supported beam. On this basis, an accurate identification method of local damage of beam structure under vehicle load is proposed. Firstly, the local bending stiffness is described in terms of equal length intervals. Secondly, the corresponding loading methods are established for single concentrated load and two-axle vehicle respectively, and the local bending stiffness values of each interval are solved by analytic equation established by node displacement. Damage information can be identified by comparing the flexural stiffness values of simply supported beams before and after damage. Based on the discreteness of local bending stiffness of simply supported beams and the change of local bending stiffness caused by damage, the location and degree of local damage of beams can be accurately identified.

Investigation of Bending Stiffness of Gas Turbine Engine Rotor Flanged Connection

ABSTRACTThe article deals with the modeling of stiffness properties of the rotors flange joints, which largely determine overall dynamics. Research is conducted on the example of the standard compressor shaft flange connection and the disk of the high-pressure turbine in the gas generator of the gas turbine engine (GTE). It is noted that the bending stiffness of the flange connection is a nonlinear function of the bending moment, whose both experimental and analysis magnitude is related to the rotor deflection from the unbalanced forces. It is shown that the value of the bending stiffness essentially depends not upon the flange connection geometry but on the bolts tightening force, the axial force, the tensile joint, the contact strain of the flange surfaces. Analysis of the effect obtained in different models of the flange connection of the bending stiffness values on the overall dynamics of the rotor showed the necessity of taking into account the entire set of factors acting in the joint.

Calculation on Bending Stiffness of RC Short Beam Strengthened by CFRP

Based on the bending tests of seven reinforced concrete (RC) short beams strengthened with carbon fiber reinforced polymer (CFRP), the bending stiffness curves of the whole process of the short beams strengthened with CFRP were obtained. The variation law of bending stiffness curve of short beam in the whole loading process was analyzed. Based on the reasonable calculation assumption, the calculation method of flexural rigidity of short reinforced concrete beams strengthened with CFRP sheets in the whole loading process was put forward. The comparison between the calculated value and the test value of bending stiffness showed that the calculation method of bending stiffness was reasonable and had high calculation accuracy. This calculation method can be used not only in the calculation of flexural rigidity of short reinforced concrete beams strengthened with CFRP sheets but also in the calculation of flexural rigidity of ordinary short reinforced concrete beams. The calculation method in this paper can provide a theoretical basis for the deformation calculation of reinforced concrete short beams strengthened with CFRP sheets.

Experimental study on flexural performance of fabricated ceramsite concrete lightweight Wall Panel

In this paper, through the mechanical property test of lightweight ceramsite concrete partition board, the bending bearing capacity of different thickness of the board is measured. Through the test, the influence of humidity on the ceramsite concrete wall panel and the vertical compressive performance of the ceramsite concrete slab are studied, and the vertical compressive bearing capacity is obtained. The results show that: the bearing capacity of different thickness wallboards used in the test is far greater than 1.5 times of the dead weight of the plates. Through the failure load of the plates, the deflection values and bending stiffness values of the wallboards in the actual engineering are obtained. The vertical allowable loads of the three thickness plates are 129.73KN, 311.90KN and 127.02KN.

Passive separation control of a NACA0012 airfoil via a flexible flap

The incorporation of nature-inspired techniques to control or reduce boundary layer separation, to bring about performance enhancements on air/water vehicles, has been an active research area for many years. In this paper, a baseline NACA0012 airfoil is modified using a short flap on its upper surface at a Reynolds number of Re = 1000. The impact of the flap configuration—described by length, attachment position, deployment angle, and material properties, on the aerodynamic performance of the airfoil—quantified by mean and fluctuating forces, is investigated, and the flow field is analyzed. Inspired by the observation of pop-up feathers on a bird’s wing, the flap is first set to be rigid for a range of location, size, and inclination angles. After the optimal location of a rigid flap has been established, the flap is then allowed to be flexible, its motion is coupled to the encircling flow field, and it is tested for a range of mass ratios and bending stiffness values. The fluid motion is obtained by solving the lattice Boltzmann equation, while the dynamics of the flexible flap are calculated using the finite element method and the coupling between the flow and flap handled by the immersed boundary method. For the flexible flap, two flapping patterns are observed and the mechanism of separation control via rigid/flexible flap is explained. Compared to the flapless NACA0012 airfoil case, in the case with a flap of optimal configuration, the mean lift coefficient is improved by 13.51%, the mean drag coefficient is decreased by 3.67%, the mean lift-drag ratio is improved by 17.84%, the maximum lift fluctuation is decreased by 40.90%, and the maximum drag fluctuation is decreased by 56.90%.

Comparison of polyglycolic acid acupoint catgut embedding therapy monofilaments for a juvenile pseudo-myopia surface modified by two processing methods

Polyglycolic acid (PGA) acupoint catgut embedding therapy (ACET) monofilament has been heavily used for juvenile pseudopia in the recent years. However, poor hydrophilicity and cytocompatibility have limited its development and wide practical application. In this context, this work is aimed to develop ACET materials with good comprehensive properties by surface modifications. Two different methods, namely ultrasound and plasma technologies, were selected to modify the surface property of PGA monofilaments to improve their wetting and compatibility with tissues, while minimizing degradation of the fibers. Moreover, the effects of these two processing methods on the structure, mechanical and in vitro properties of PGA were fully characterized. Both the ultrasound and plasma modified samples were observed to have a larger surface roughness, and their weights and diameters were decreased. Samples P-PGA1 (76.2° ± 1.4°) and P-PGA2 (73.5° ± 1.9°) exhibited the smallest contact angle values among their groups, respectively. The tensile properties and bending stiffness values of modified PGA decreased slightly, while their swelling ratios were greatly improved. All the prepared samples presented no toxicity (more than 75% cells being viable), and their cell attachment ratios (cultured for 48 h) were also enhanced. In summary, plasma and ultrasound modified PGA showed better hydrophilicity and in vitro properties compared to that of unmodified samples, while retaining the other excellent characteristics. These findings illustrated that the two processing methods were feasible and warrant further study in the application of ACET materials.

Structural Damage Identification of Bridges from Passing Test Vehicles.

This paper presents two approaches for the structural damage identification of a bridge from the dynamic response recorded from a test vehicle during its passage over the bridge. Using the acceleration response recorded by the vibration sensors mounted on a test vehicle during its passage over the bridge, along with the computed displacement response, the bending stiffness of the bridge can be determined using either: (1) the frequency-domain method based on the improved directed stiffness method with the identified frequency and corresponding mode shape, or (2) the time-domain method based on the residual vector of the least squares method with a fourth-order displacement moment. By comparing the bending stiffness values identified from the vehicle-collected data for the bridge under the undamaged and damaged states that are monitored regularly by the test vehicle, the bridge damage location and severity can be identified. Through numerical simulations and field tests, the present approaches are shown to be effective and feasible.

A study of ultrasound/H2O2 combined surface modification on polyglycolic acid monofilaments for acupoint catgut embedding therapy application

Polyglycolic acid (PGA) monofilament has been regarded as an excellent acupoint catgut embedding therapy (ACET) material because it offers numerous advantages, including easy accessibility and good forming and degradable properties. However, the poor hydrophilicity and cytocompatibility are the main disadvantages preventing it from having wider applications. In this communication, two types of PGA monofilaments were first fabricated from their polymer chips, followed by ultrasound/H2O2 combined surface modification at 1:1 (V/V), and different ultrasound frequencies (45, 60 and 75 KHz) were explored. The modified PGA monofilaments were fully characterized with respect to structure characterizations (surface morphology, weights and diameters, Fourier transform infrared spectroscopy (FT-IR) analysis and hydrophilicity), mechanical properties (tensile property, swelling behavior and flexibility) and in vitro properties (cytotoxicity, cell attachment and cell morphology). The results showed that the PGA monofilaments after modification would become coarser, with larger weights and diameters. Samples 1-PGA 75 and 2-PGA 75 exhibited the smallest contact angles at 70.51° ± 3.27° and 62.84° ± 2.53°, respectively. The FT-IR analysis results confirmed that some polar groups emerged, promoting the hydrophilicity of PGA monofilaments. The swelling behavior of monofilaments was enhanced, while tensile and bending stiffness values slightly decreased. All the prepared samples presented no toxicity, and the cell attachment ratio (cultured for 48 h) of PGA monofilaments had been greatly improved after modification. These findings present important clinical implications in the ACET materials manufacturing process and warrant further study to develop new PGA embedding materials with outstanding clinical efficacy.

Study on behaviour of geometrically scaled glass reinforced epoxy tubes subjected to non-coincident quasi static-indentation

PurposeThe purpose of this paper is to study the behaviour of glass reinforced epoxy tubes subjected to repeated indentation loads at two non-coincident indentations 180° apart.Design/methodology/approachFour geometrically scaled specimens ranging from 100 to 400 mm diameter were used in repeated indentation tests. Force, displacement and damage growth were recorded for loading and unloading until the indenter returned to its original starting point.FindingsSimilar scaled trends were observed between the non-coincidental loadings. Unlike reported response form coincidental loadings, the responses from non-coincidental loadings yield lower values for bending stiffness and peak load.Research limitations/implicationsThe differences in behaviour of the specimen between non-coincident loadings were attributed to reductions in fracture toughness and circumferential modulus.Practical implicationsDistant non-interacting damage and delamination around the circumference does reduce the structural performance.Originality/valueBehaviour of composite tubes under different loading conditions, for example low speed impact or quasi static indentation, is widely studied, however little attention has been given to the repeated loading incidents.